M29: large tool response offload to filesystem #791
Description
Offload large tool responses to temp files instead of keeping in context or zeroing out.
Gap: Zeph has no offload mechanism — large outputs stay in context or get body-zeroed losing information. Responses exceeding a threshold should be written to temp files with a pointer retained in context.
Acceptance Criteria
- Implement response offload with configurable threshold
- Add config.toml options for offload threshold and retention
- Implement cleanup for expired offload files
Ref: .local/plan/m27-m31-context-memory-improvements.md